help needed for new headphone system

I’ve had as high end a headphone system as I could afford for nearly fifty years. I got serious into digital (sources for my headphone system)  about fifteen years ago. I went through a dozen headphones, and amps, and sources. Given where you are... I would say your headphones are plenty capable. 

The primary determinant in the sound is the headphone amp. Headphones vary in requirements tremendously. But respond really well to massive power. As I said, I have had many head amps. My system got tremendously better when I found Woo headphone amps. Lots of natural musical power. If you start with a really good powerful headphone amp... your headphones are going to sound incredible... then you can add other improvements. I have a Woo WA5... it simply took my system a couple levels beyond where it was... and it was already very good by nearly anyones standards. I would get the best Woo head amp (not WA6... too little power) and a BlueSound streamer. That will improve your system by and order of magnitude. But go all in on a great head amp... I spent thousands on different high end headphones and different amps... one can save a lot of money by one bold move. You can fool around spending lots of money and not get there. 

You can see my headphone system under User ID in virtual systems. I replaced the stock 300B tubes with Takitsuki ($1K each... incredible... but later). 

You need to hear as much as you can of alternatives on the market.  The best way to do that is to go to a major regional audio show.  At these shows, there is a section where headphone people display their wares.  Even if you are not a headphone nut,, this is a fun place to visit at shows.  The people are friendly and they allow you to try different combination of gear, even if that means taking something to another booth/table to try out.

@ghdprentice Thanks very much, that it exactly the advice I was looking for.  Woo has a big presence at Axpona but I didn't spend any time with them , unfortunately. I'll do some research on their product line.

@larryi As I posted, I spent time at the last two Axpona conventions listening to headphones.  For me that was simply not helpful .   Thanks for the advice, though.

@treepmeyer go to a CANJAM or a shop to demo stuff. Strangers with different hearing abilities and sensibilities will just give you recommends of what they own or like. I'd rather you go listen. Also the Qudelix can be used wired, I have one with my IEM.

And frankly getting an "upgrade" to your Sennheiser will be hard. You're better of testing parametric EQ presets and trying to EQ to your individual pHRTF

 The ABSOLUTE best "BBC" sound I have ever heard from headphones are those using Bio Cellulose drivers like the ZMF "Atrium & Auteur"..These drivers create a sound that is warm,lush,organic & dripping with ambiance..Be warned though,they take hundreds of hours use to come into true voice & they pair best with neutral source gear..They can become far too dark & obscure fine detail when driven by warm amplifiers & shine with great Class A Solid State like SPL,Denafrips etc...
You should also spend time going through the gear reviews on head-fi.org....